1. Field of the Invention
The present invention relates to a cathode ray tube (CRT), and more particularly, to a tensioned shadow mask with a color selection function.
2. Description of the Related Art
CRTs for television and computer displays employ a faceplate having on the inner side thereof a phosphor screen with a predetermined pattern, a mask and frame assembly which is an assembly of a shadow mask (hereinafter, simply referred to as a mask) and a frame, and is installed on the inner side of the faceplate, a funnel connected to the faceplate, which has a neck portion and a cone portion, and an electron gun inserted in the neck portion of the funnel, for emitting electron beams through apertures of the mask to excite the phosphor screen, and a deflection yoke installed around the cone portion of the funnel, for deflecting electron beams from the electron gun.
In a CRT having the above configuration, the mask for accurate landing of three electron beams emitted from the electron gun on each phosphor layer of the phosphor screen includes; a dot mask with substantially circular apertures a slot mask with parallel elongated apertures, and a tensioned mask to which tension is applied from opposite sides thereof, and having a series of parallel stripes separated by slits through which electron beams pass.
FIG. 1 shows an example of a tensioned mask. As shown in FIG. 1, the tensioned mask includes a plurality of strips 22 separated by slits 21 having a predetermined interval, and a plurality of tie bars 33 which interconnect the adjacent strips. The tensioned mask is supported in tension by a frame (not shown) of the tensioned mask.
In the mask, the tie bars 23 which interconnect the adjacent strips 22 can reduce a howling phenomenon, which occurs due to mask vibration from external impact, and unacceptable Poisson""s contraction. However, if the vertical pitch of the tie bars 23 is too large, that is, if the vertical pitch (PV) of the tie bars 23 is twice or more the horizontal pitch (PH) thereof, a reflection image of the tie bars 23 is shown on the screen, which is unpleasant to viewers.
To avoid this problem, U.S. Pat. No. 4,926,089 discloses a tensioned mask as shown FIG. 2. As shown FIG. 2, the tensioned mask includes a plurality of strips 31 separated by slits 32 having a predetermined interval, and tie bars 33 which interconnect the adjacent strips 31. Also, dummy bridges 34, which extend partially between but not interconnecting adjacent strips, are disposed between the adjacent tie bars 34 and separate each slit 32 into sub-slits having a predetermined interval.
In the tensioned mask, due to a technical problem in mask pattern formation, the width W1 of the dummy bridges 34 is smaller than the width W2 of the tie bars 33. Thus, the reflection images by the dummy bridges 34 and the tie bars 33 have a slight difference in intensity of light. This difference raises the problem of tie bar visibility, thus deteriorating display image and making viewing unpleasant.
To solve the above problems, an object of the present is to provide a tensioned shadow mask for a cathode ray tube (CRT), capable of eliminating the problem of tie bar visibility while enhancing display image visibility.
In one embodiment of the present invention, there are provided a tensioned shadow mask for a CRT, comprising: a series of parallel strips separated by slits having a predetermined interval; a plurality of tie bars interconnecting adjacent strips to define a plurality of slits at predetermined intervals; and a plurality of dummy bridges disposed between adjacent tie bars, extending from one of the strips to the other but not interconnecting the adjacent strips, wherein the dummy bridges are longer than the tie bars in the longitudinal direction of the strips.
In the tensioned shadow mask according to the present invention, the area of the dummy bridges is equal to that of the tie bars, or the area difference between the dummy bridges and the tie bars is in a predetermined range. The dummy bridges may extend from a strip to the next strip but not intersecting the adjacent strips, or the dummy bridges may alternately extend from the adjacent strips such that a first dummy bridge extends from one of the adjacent strips and the next dummy bridge extends from the other of the adjacent strips.